X-ray image diagnostic apparatus

ABSTRACT

An X-ray image diagnostic apparatus including an X-ray source, an X-ray flat panel detector, an image processor, and an image display. The image processor includes a storage for storing plural sets of residual image data, acquired in advance from X-ray images in X-ray image acquisition modes from the X-ray flat panel detector before an actual measurement, in correspondence with the X-ray image acquisition modes, and a residual image corrector for correcting residual image data contained in an X-ray image in the actual measurement from the X-ray flat panel detector, using the residual image data stored in the storage.

TECHNICAL FIELD

The present invention relates to an X-ray image diagnostic apparatusthat performs multiple radiography or fluoroscopy continuously, and toan X-ray image diagnostic apparatus in which a residual image of anX-ray image obtained by current radiography or fluoroscopy is correctedin real time.

BACKGROUND ART

An X-ray image diagnostic apparatus adopts an X-ray flat panel detectorhaving an X-ray detector made of amorphous silicon, and residual imagecorrection is necessary for the X-ray flat panel detector.

One example of residual image correction is described inJP-A-2001-243454 (public known reference). More specifically, aworkstation takes samples on image data from a digital detectorfollowing the completion of first X-ray irradiation, so that attenuationof a residual image phenomenon is modeled. The workstation then predictsfurther attenuation of the residual image phenomenon on the basis of themodeled attenuation. The workstation thus corrects or compensates forattenuation of the residual image phenomenon in the following X-rayirradiation on the basis of the predicted attenuation.

The public known reference cited above, however, is silent aboutperforming residual image correction in real time, because a predictionis made by acquiring residual image data, and processing time isnecessary for acquisition and prediction.

DISCLOSURE OF THE INVENTION

An X-ray image diagnostic apparatus of the invention includes: an X-raysource that irradiates X-rays to a subject; an X-ray flat panel detectorthat is provided oppositely to the X-ray source and detects transmittedX-rays from the subject as an X-ray image; image processing means forapplying image processing to the X-ray image detected by the X-ray flatpanel detector; and image display means for displaying the X-ray imagehaving undergone the image processing in the image processing means. Theimage processing means includes: storage means for storing plural setsof residual image data, acquired in advance from X-ray images in X-rayimage acquisition modes from the X-ray flat panel detector before anactual measurement, in correspondence with the X-ray image acquisitionmodes; and residual image correction means for correcting residual imagedata contained in an X-ray image in the actual measurement from theX-ray flat panel detector, using the residual image data stored in thestorage means.

It is thus possible to perform residual image correction of an X-rayimage in real time.

According to one preferred embodiment of the invention, the imageprocessing portion includes: an image memory that stores one frame ofthe residual image data from the X-ray flat panel detector; anattenuation quantity storage portion that stores quantities ofattenuation of first and subsequent frames of the residual image dataread out from the image memory; a computing unit that reads out thequantities of attenuation of the first and subsequent frames of theresidual image data in response to a time on the basis of one frame ofthe residual image data stored in the image memory, and subtracts theread quantities of attenuation of the residual image data from a signaloutputted from the X-ray flat panel detector; and a control portion thatcontrols the image memory, the attenuation quantity storage portion, andthe computing unit on the basis of respective signals, including controlsignals for each of the X-ray image acquisition modes including aradiographic signal and a fluoroscopic signal, and an imagesynchronizing signal to enable a display on the display means.

It is thus possible to address the attenuation characteristic of aresidual image that varies in real time.

According to one preferred embodiment of the invention, the storagemeans stores plural frames of images of a residual image while X-raysare shielded after an X-ray image is acquired at a specific X-ray dosein advance.

It is thus possible to read out the residual image from the storagemeans according to the image synchronizing signal.

According to one preferred embodiment of the invention, the imageprocessing means includes: plural image memories, each of which storesone frame of residual image data from the X-ray flat panel detector;plural attenuation quantity storage portions that store quantities ofattenuation of first and subsequent frames of the residual image dataread out from the image memories; a weight addition quantity storageportion that reads out quantities of attenuation of the first andsubsequent frames of the residual image data in response to a time onthe basis of one frame of the residual image data stored in each of theimage memories, subjects the read quantities of attenuation of residualimages to weighting addition depending on magnitude of a quantity ofremaining residual images, and stores weight addition quantities; acomputing unit that reads out the weight addition quantities stored inthe weight addition quantity storage portion in response to a time, andsubtracts the read weight addition quantities from a signal outputtedfrom the X-ray flat panel detector; and a control portion that controlsthe image memories, the attenuation quantity storage portions, and theweight addition quantity storage portion on the basis of respectivesignals, including control signals for each of the X-ray imageacquisition modes including a radiographic signal and a fluoroscopicsignal, and an image synchronizing signal to enable a display on thedisplay means.

It is thus possible to perform the residual image correction processingcorresponding to the attenuation characteristic of a residual image thatvaries in real time even when a multiple-composite residual image ispresent.

According to one preferred embodiment of the invention, the imageprocessing portion includes: an image memory that stores one frame ofresidual image data from the X-ray flat panel detector; a first switchthat switches an output of a quantity of attenuation of an image of aresidual image read out from the image memory depending on a read pixelmatrix of the X-ray flat panel detector; plural attenuation quantitystorage portions, each of which stores quantities of attenuation offirst and subsequent frames of the residual image data on the basis ofone frame from the image memory switched by the first switch, incorrespondence with the read pixel matrix of the X-ray flat paneldetector; a second switch that reads out a quantity of attenuation of aresidual image stored in the attenuation quantity storage portions inresponse to a time, and makes a switch to the read quantity ofattenuation of the residual image data; a computing unit that subtractsthe quantity of attenuation of the residual image data switched by thesecond switch from a signal outputted from the X-ray flat paneldetector; and a control portion that controls the image memory, theattenuation quantity storage portions, and the first and second switcheson the basis of respective signals, including control signals for eachof the X-ray image acquisition modes including a radiographic signal anda fluoroscopic signal, and an image synchronizing signal to enable adisplay on the display means.

It is thus possible to perform the residual image correction processingcorresponding to the attenuation characteristic of a residual image thatvaries in real time even when the pixel unit read out from the X-rayflat panel detector is different.

According to one preferred embodiment of the invention, the imageprocessing means includes: an image memory that stores one frame ofresidual image data from the X-ray flat panel detector; a first switchthat switches an output of a quantity of attenuation of a residual imageread out from the image memory depending on whether the X-ray imageacquisition mode is a single radiographic mode or a continuousradiographic mode; plural attenuation quantity storage portions, each ofwhich stores quantities of attenuation of first and subsequent frames ofthe residual image data on the basis of one frame from the image memoryswitched by the first switch, in correspondence with the singleradiographic mode and the continuous radiographic mode; a second switchthat reads out a quantity of attenuation of the residual image stored inthe attenuation quantity storage portions in response to a timedepending on the single radiographic mode or the continuous radiographicmode, and makes a switch to the read quantity of attenuation of theresidual image; a computing unit that subtracts the quantity ofattenuation of the residual image switched by the second switch from asignal outputted from the X-ray flat panel detector; and a controlportion that controls the image memory, the attenuation quantity storageportions, and the first and second switches on the basis of respectivesignals, including control signals for each of the X-ray imageacquisition modes including a radiographic signal and a fluoroscopicsignal, and an image synchronizing signal to enable a display on thedisplay means.

It is thus possible to perform the residual image correction processingcorresponding to the attenuation characteristic of a residual image thatvaries in real time even the X-ray image acquisition mode is theradiographic mode that continues several times.

According to one preferred embodiment of the invention, the controlportion determines a quantity of the residual image generated fromcontinuous exposures in response to an exposure time in the continuousradiographic mode.

It is thus possible to perform the residual image correction processingcorresponding to the attenuation characteristic of a residual image thatvaries in real time while taking a factor of a time of the radiographicmode that continues plural times into account.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram common in respective embodiments of an X-rayimage diagnostic apparatus of the invention;

FIG. 2 is a block diagram showing a residual image correction processingportion incorporated in an image processing portion of FIG. 1;

FIG. 3 is a view showing one example of residual image time attenuationfactors stored in an attenuation table of FIG. 2 in graph form;

FIG. 4 is a block diagram showing an example of the configuration of theresidual image correction processing portion when the following exposureis performed before a residual image disappears;

FIG. 5 is a block diagram showing an example of the configuration of theresidual image correction processing portion in which (1×1) to read outpixels one by one and (2×2) to average four pixels and read them out asa whole as one pixel are attenuation tables;

FIG. 6 is a block diagram showing an example of the configuration of theresidual image correction processing portion capable of correctingresidual images in both a non-continuous radiography (single) and acontinuous radiography; and

FIG. 7 is a view used to describe an example of settings of selectionconditions of residual images stored in attenuation tables 1 through 4for the continuous radiography of FIG. 6.

BEST MODE FOR CARRYING OUT THE INVENTION

Hereinafter, preferred embodiments of an X-ray image diagnosticapparatus of the invention will be described in detail with reference tothe accompanying drawings.

As is shown in FIG. 1, an X-ray image diagnostic apparatus comprises anX-ray source 3, such as an X-ray tube, that generates X-rays, an X-rayflat panel detector 4 placed oppositely to the X-ray source 4, a C-arm 5that supports the X-ray source 4 and the X-ray flat panel detector 3, aleg portion 6 that holds the C-arm 5 to stand on the floor, an X-raygeneration high-voltage power source 7 that is electrically connected tothe X-ray source 4, an image processing portion 8 that is electricallyconnected to the X-ray flat panel detector 3, and an image displayportion (monitor) 9 that is electrically connected to the imageprocessing portion 8.

The X-ray source 3 irradiates X-rays to a subject 1 lying on adiagnostic table 2. Conditions of the X-ray irradiation areconditionally selected by an operator using an unillustrated operationconsole or the like. The conditional-selection relates to X-rayirradiation conditions in X-ray image acquisition modes, for example,the fluoroscopic mode and the radiographic mode.

The X-ray flat panel detector 4 detects X-rays having passed through thesubject 1 as an X-ray image. The conditions of the X-ray detection areconditionally selected by the operator of the apparatus using theunillustrated operation console or the like as with the case of theX-ray source 3. The conditional-selection relates to X-ray detectionconditions in the X-ray image acquisition modes, and includes, forexample, a (1×1) mode to read out detection elements that form the X-raydetector one by one, and a (2×2) mode to read out the detection elementsalternately. The X-ray flat plane detector 4 is one example of the X-raydetector, and is formed by laminating scintillator and amorphoussemiconductor. Also, the X-ray detector is not limited to the X-ray flatpanel detector 4, and any detector of a type in which detection ofX-rays gives rise to a residual image is included in a techniquedisclosed in this embodiment.

The C-arm 5 is supported on the leg portion 6, and is able to rotate andmove in parallel while maintaining the X-ray source 3 and the X-ray flatpanel detector 4 in the relation of being oppositely placed. The X-raygeneration high-voltage power source 7 supplies the X-ray source 4 withpower. The image processing portion 8 receives an X-ray image detectedin the X-ray flat panel detector 4 as an input, and performs imageprocessing, such as filtering, so that an X-ray image suitable fordiagnosis is displayed on the monitor 9. The image processing portion 8includes a memory to store an image to be processed. The monitor 9displays an X-ray image having undergone image processing in the imageprocessing portion 8.

A residual image correction processing portion shown as the firstembodiment is incorporated in the image processing portion 8. As isshown in FIG. 2, the residual image correction processing portionincludes an image memory 10 that is electrically connected to the X-rayflat panel detector 4, an attenuation table 11 that is electricallyconnected to the image memory 10, a computing unit 12 that iselectrically connected to the X-ray flat panel detector 4 and theattenuation table 11, and a control portion 13 that is electricallyconnected to respective signals, including control signals for therespective modes, such as a radiographic signal and a fluoroscopicsignal, and an image synchronizing signal that enables a display on themonitor 9, and is also electrically connected to the image memory 10,the attenuation table 11, and the computing unit 12.

The image memory 10 stores an image in the fluoroscopic (radiographic)mode after X-ray irradiation ends in the radiographic (fluoroscopic)mode and before X-ray irradiation starts by switching to thefluoroscopic (radiographic) mode, that is, it stores one frame of aresidual image. The image memory 10 acquires residual image datacorresponding to an X-ray dose incident on the X-ray flat panel detector3 during an exposure by storing an image after a pre-set time from theend of the exposure. The residual image data thus acquired is stored inthe image memory 10 according to a radiographic signal (fluoroscopicsignal) outputted from the X-ray generation high-voltage power source 7.The attenuation table 11 stores, as the attenuation characteristic,quantities of attenuation corresponding to the pixel positions of afluoroscopic image immediately after an image of the residual image isstored in the image memory 10, that is, from first and subsequentframes. The attenuation characteristic can be visualized in graph formas shown in FIG. 3, using the ordinate for a quantity of attenuation andthe abscissa for a time elapsed since the residual image was stored inthe image memory 10 (number of frames). An exposure is performed at aspecific X-ray dose in advance, and images of a residual image of pluralframes are stored successively in the attenuation table 11 while X-raysare shielded, so that quantities of attenuation of these images of theresidual image can be read out in response to a specific X-ray dose. Thespecific X-ray dose referred to herein is determined by various X-raydoses assumed in fluoroscopy or radiography. That is, by measuringresidual image data while varying an X-ray dose in various manners, itis possible to create an attenuation table corresponding to the residualimage data that differs with a varied X-ray dose. Plural frames ofresidual image data that keeps varying can be thereby acquired accordingto the image synchronizing signal. The computing unit 12 subtracts theresidual image data that attenuates with time as is shown in theattenuation table from a fluoroscopic image after the exposure. Afluoroscopic image from which the residual image is removed or reducedcan be thus found.

Operations of the X-ray image diagnostic apparatus of the firstembodiment will now be described. Herein, a case where the X-ray imageacquisition mode, in which an X-ray image is acquired, is switched fromthe radiographic mode to the fluoroscopic mode will be described. Theattenuation table 11 has stored images (images of an attenuatingresidual image) in the last or before the last radiographic mode thatattenuate with time. The images of the attenuating residual image keepattenuating with time since the mode is switched to the fluoroscopicmode. The X-ray source 3 irradiates X-rays to the subject 1 lying on thediagnostic table 2 under the X-ray irradiation conditions in thefluoroscopic mode. The X-ray flat panel detector 4 detects X-rays havingpassed through the subject 1 as a fluoroscopic image. The residual imagecorrection processing portion stores a residual image after a pre-settime since the last or before the last X-ray image acquisition mode (forexample, radiographic mode) ended, frame by frame in the image memory10. The image of the residual image stores a radiographic signal or afluoroscopic signal outputted from the X-ray generation high-voltagepower supply 7. The computing unit 12 subtracts a quantity ofattenuation of the residual image from the fluoroscopic image on which aquantity of the residual image corresponding to the frames after theradiographic mode is superimposed, and thereby finds a fluoroscopicimage from which the residual image is reduced or removed. The monitor 9displays the fluoroscopic image from which the residual image is reducedor removed.

As has been described, according to the X-ray image diagnostic apparatusof the first embodiment, it is possible to address the attenuationcharacteristic of a residual image that varies in real time. To be moreconcrete, the residual image correction processing portion includes theattenuation table 11 having stored attenuation information of pluralresidual images in the X-ray flat panel detector 4 that correspond tothe respective fluoroscopic and radiographic modes, and the computingunit 12 that performs correction computation of a residual image thatattenuates with time on the basis of the attenuation information of theresidual images in the X-ray flat panel detector 4 stored in theattenuation table 11. The computing unit 12 therefore carries outcorrection computation of the residual image that attenuates with timeon the basis of the attenuation information of the plural residualimages in the X-ray flat panel detector 4 corresponding to therespective fluoroscopic and radiographic modes stored in the attenuationtable 11. It is thus possible to perform residual image correctionprocessing corresponding to the attenuation characteristic of a residualimage that varies in real time.

A case where a second radiographic mode is performed while a residualimage of a first radiographic mode is present, and a fluoroscopic modeis further performed in a third exposure will now be described as asecond embodiment with reference to FIG. 4. Herein, a residual imagethat resides due to the first radiographic mode is also referred to as asecondary residual image. Differences of the second embodiment from thefirst embodiment can be readily understood as follows by comparing FIG.2 with FIG. 4. Differences are: two image memories 10 a and 10 b and twoattenuation tables 11 a and 11 b are included instead of the imagememory 10 and the attenuation table 11; a weighting table 14 that storesthe two attenuation tables 11 a and 11 b after weighting processing isincluded; and the computing unit 12 finds residual image data that needsto be removed, from a result of the weighting addition processing usingthe weighting table 14. This is the case where two attenuation tablesare prepared; however, the invention is not limited to thisconfiguration. Three or more attenuation tables may be prepared, so thatresidual image data that needs to be removed is found from a result ofweighting addition of respective results.

Operations of the X-ray image diagnostic apparatus of the secondembodiment will now be described. In a first radiographic mode, thecontrol portion 13 controls the weighting table 14 to output all theoutputs from the attenuation table 11 a to the computing unit 12. When asecond radiographic mode is performed subsequently, an image of aresidual image is recorded in the image memory 10 b, and a quantity ofthe residual image is computed using the attenuation table 11 bseparately from a calculation of a quantity of the residual image usingthe image of the residual image recorded in the image memory 10 a, andthe result of computation is outputted to the weighting table 14. In theweighting table 14, a weight to a quantity of the residual image in thesecond exposure is increased for an image region where there are no orfewer residual image components of the first exposure. In a case wherethere are many residual image components in the first radiographic mode,and residual image components in the second radiographic mode are fewer,a weight of the residual image components in the first radiographic modeis increased. In short, a weight can be added in response to quantitiesof residual image components in the first radiographic mode and residualimage components in the second radiographic mode.

As has been described, according to the X-ray image diagnostic apparatusof the second embodiment, even when a multiple-composite residual imageis present, it is possible to provide an X-ray image diagnosticapparatus capable of performing residual image correction processingcorresponding to the attenuation characteristic of a residual image thatvaries in real time. To be more concrete, even when a composite residualimage, resulted from a case where the second radiographic mode iscarried out before a residual image of the first radiographic modedisappears completely, gives influences to a fluoroscopic mode carriedout in a third exposure, it is possible to achieve residual imagecorrection processing corresponding to the attenuation characteristic ofa residual image that varies in real time.

Also, about 120 to 150 sec. later, a quantity of the residual imageoften gives substantially no influences to the following X-ray imageacquisition mode. Hence, in a case where the radiographic mode and thefluoroscopic mode are repeated frequently, by omitting weightingaddition in the X-ray image acquisition mode that no longer givesinfluences, a quantity of the composite residual image can be found athigh speeds by weighting addition.

A case where a pixel unit read out from the X-ray flat panel detector isdifferent will now be described as a third embodiment with reference toFIG. 5. Herein, in a case where an image of the same portion of thesubject is to be acquired, a high-definition fluoroscopic mode (1×1 readfluoroscopic mode) by which, although a display speed is slow due to alarge volume of process data involved in image display, a fluoroscopicimage can be obtained at high definition, and a fast fluoroscopic mode(2×2 read fluoroscopic mode) by which, although definition isdeteriorated due to a small volume of process data involved in imagedisplay, a fluoroscopic image can be obtained at a high display speed,will be described by way of example. The 1×1 read fluoroscopic mode is amode by which respective detection elements forming the X-ray flat paneldetector are read out one by one. The 2×2 read fluoroscopic mode is amode by which four pixels of each 2×2 matrix of respective detectionelements forming the X-ray flat panel detector are added up, and aresultant added one pixel is read out. A data volume is thereforereduced to ¼ of that in the 1×1 read fluoroscopic mode. In addition, thehigh-definition fluoroscopic mode and the fast fluoroscopic mode ingeneralized versions of the foregoing are not limited to 1×1 and 2×2,and can be applied to various pixel sizes of 3×3, 4×4, etc.

Differences of the third embodiment from the first embodiment can bereadily understood as follows by comparing FIG. 2 with FIG. 5.Differences are: attenuation tables 11 c and 11 d, respectively, for the1×1 read fluoroscopic mode and the 2×2 read fluoroscopic mode areincluded instead of the attenuation table 11; multiplexers 15 a and 15 bthat switch an image signal for each pixel read unit of the X-ray flatpanel detector are included; an averaging unit 16 that averages fourpixels of 1×1 for residual image data in the 1×1 read fluoroscopic modeto be used in the 2×2 read fluoroscopic mode, is included; the computingunit 12 finds a residual image that needs to be removed using readpixels switched by the multiplexer 15 b; and the control portion 13additionally receives, as an input, a fluoroscopic mode signal thatdetermines 1×1 or 2×2 read pixels, and the control portion 13 operatesaccording to the input signal.

Operations of the X-ray image diagnostic apparatus of the thirdembodiment will now be described. When the 2×2 read fluoroscopic mode iscarried out after an exposure, the control portion 11 controls themultiplexer 15 a in such a manner that an output from the image memory10 is inputted to the attenuation table 11 d for the 2×2 readfluoroscopic mode. Correction means same as in the first embodiment isthus applied to an image in the 2×2 read fluoroscopic mode. Likewise,when the 1×1 read fluoroscopic mode is carried out, the control portion13 controls the multiplexer 15 a in such a manner that an output fromthe image memory 10 is inputted to the attenuation table tic for 1×1.Correction means same as in the first embodiment is thus applied to animage in the 1×1 read fluoroscopic mode. Incidentally, when the readpixel size is changed during fluoroscopy, conversion is necessarybecause an image recorded in the image memory 10 and a fluoroscopicimage that needs correction are of different sizes. When the 2×2 readfluoroscopic mode is carried out before an exposure, residual image datain the 2×2 read fluoroscopic mode is recorded in the image memory 10.Likewise, when the 1×1 read fluoroscopic mode is carried out, residualimage data in the 1×1 read fluoroscopic mode is recorded in the imagememory 10. Normally, fast processing is required for a fluoroscopicimage, and an input to the image processing portion 8 is handled in asize of the 2×2 read fluoroscopic mode. The image memory 10 thereforehas a recording size of the 2×2 read fluoroscopic mode, too. In thiscase, when the fast fluoroscopic mode is switched to the high-definitionfluoroscopic mode, the 2×2 read fluoroscopic mode is carried out beforean exposure, and the 2×2 read fluoroscopic mode is changed to the 1×1fluoroscopic mode after the exposure. Of the residual image datarecorded in the image memory 10, data of an image region in the 1×1 readfluoroscopic mode is sent to the attention table 11 c for the 1×1 readfluoroscopic mode. This is because when data of the image region aloneis sent, high definition is maintained and yet a rate of processingspeed can be taken into account by optimizing a data volume. In thisinstance, a single pixel in the residual image data in the 2×2 readfluoroscopic mode stored in the image memory 10 is inputted to fourpixels at positions corresponding to this pixel in the residual imagedata in the 1×1 read fluoroscopic mode within the attenuation table 12.Also, the 1×1 read fluoroscopic mode is carried out before an exposure,and 1×1 exposure is carried out subsequently. Further, when the 1×1 readfluoroscopic mode is changed to the 2×2 read fluoroscopic mode afterthis exposure, neighboring four pixels within the record memory 10 areaveraged before being input to the attenuation table, and then outputtedto the 2×2 attenuation table 11 d.

As has been described, according to the X-ray image diagnostic apparatusof the third embodiment, even when a pixel unit read out from the X-rayflat panel detector is different, it is possible to perform residualimage correction processing corresponding to the attenuationcharacteristic of a residual image that varies in real time.

A case where the radiographic mode is continued will now be described asa fourth embodiment with reference to FIG. 6. Herein, cases where theradiographic mode, in which a considerable residual image resides, iscarried out a single time and repeated plural times will be describedseparately.

Differences of the fourth embodiment from the first embodiment can bereadily understood as follows by comparing FIG. 2 with FIG. 6.Differences are: an attenuation table 111 for a single radiographic modeand attenuation tables 1 through 4 (112 to 115) for a continuousradiographic mode are included instead of the attenuation table 11;multiplexers 15 c and 15 d that switch an image signal to the table forthe single radiographic mode or to the tables 1 through 4 for thecontinuous radiographic mode are included; the computing unit 12 removesa residual image in the single radiographic mode or the continuousradiographic mode switched by the multiplexer 15 d; the control portion13 receives, as inputs, the number of continuous exposures together withan exposure time of each, and operates according to the input signal;and a decision table that generates a selection signal of themultiplexers 15 c and 15 d using an output signal from the controlportion 13, is included.

Operations of the X-ray image diagnostic apparatus of the fourthembodiment will now be described. An image of the residual image in afirst radiographic mode is recorded in the image memory 10, the residualimage data is found using the attenuation table 111, and a fluoroscopicimage from which the residual image is removed is outputted bysubtracting the resultant residual image data from the fluoroscopicimage, all of which are the same as in the first embodiment. In thisembodiment, attenuation coefficients for a single radiography same asthose in the first embodiment are stored in the attenuation table 111.As are shown in FIG. 6, different tables, each having differentattenuation factors for a continuous radiography, are inputted into theattenuation tables 112, 113, 114, and 115. For the continuousradiography, an image memory value, an incident dose, an elapsed timesince the exposure, the number of exposures, and intervals of exposuresare necessary as parameters to specify the attenuation factor. Of these,an image memory value, an incident dose, and an elapsed time since theexposure are also used in the attenuation table for the singleradiographic mode. Hence, the number of exposures and intervals ofexposures are also necessary as parameters for the attenuation tablesfor the continuous radiographic mode. However, it is difficult toinclude a table having all these parameters in terms of packaging of thecircuit, and exact correction using the number of exposures andintervals of exposures is enabled by preparing plural attenuation tablesfor the continuous radiographic mode.

As has been described, according to the X-ray image diagnostic apparatusof the fourth embodiment, even when the X-ray image acquisition mode isthe radiographic mode that continues plural times, it is possible toperform residual image correction processing corresponding to theattenuation characteristic of a residual image that varies in real time.

A case where four attenuation tables 112 through 115 for the continuousradiography as are shown in FIG. 7A will now be described. An evaluationfunction, to which a weight is added at every certain time before thefluoroscopy begins, is used as a selection method of respective tables.This method will now be described.

Let a function f(x) expressed as Equation (1) be an evaluation function:f(x)=5f0+2f1+1f2   (1)where f0, f1, and f2 are the number of exposures in times t0, t1, and t2obtained by dividing a time immediately before the exposure ends.

In a case where 14 exposures are performed continuously for 25 sec. asis shown in FIG. 7B, the time is divided to 20 sec., 10 sec., and 5sec., and how many times exposures are performed within each dividedtime is stored. When two in f0, seven in f1, and three in f2, thenf(x)=5×2+2×7+1×3=27 sec.

This value is inputted into a decision table 17 shown in FIG. 7C, and acontinuous table corresponding to f(x) is selected. For example, when0≦f(x)≦10, the continuous table 1 is selected, and when 11≦f(x)≦20, thecontinuous table 2 is selected. The residual image data selected duringthe continuous radiography is thus determined.

It is thus possible to perform residual image correction processingcorresponding to the attenuation characteristic of a residual image thatvaries in real time while taking into account a factor of the time forthe radiographic mode that continues plural times.

Also, by increasing the attenuation tables for the continuousradiography as needed, exact correction is enabled for each interval ofexposures and each number of exposures.

In plural embodiments described above, for an examination of a digestivetube or the like, the need to acquire a current fluoroscopic imageimmediately after the acquisition of an image of the last exposure canbe satisfied.

Further, in the plural embodiments described above, it is possible toaddress a composite residual image resulted from multiple radiography orand fluoroscopy.

INDUSTRIAL APPLICABILITY

The invention provides an X-ray image diagnostic apparatus capable ofperforming residual image processing corresponding to the attenuationcharacteristic of a residual image that varies in real time.

1. An X-ray image diagnostic apparatus, characterized by comprising: anX-ray source that irradiates X-rays to a subject; an X-ray flat paneldetector that is provided oppositely to the X-ray source and detectstransmitted X-rays from the subject as an X-ray image; image processingmeans for applying image processing to the X-ray image detected by theX-ray flat panel detector; and image display means for displaying theX-ray image having undergone the image processing in the imageprocessing means, wherein the image processing means includes: storagemeans for storing plural sets of residual image data, acquired inadvance from X-ray images in X-ray image acquisition modes from theX-ray flat panel detector before an actual measurement, incorrespondence with the X-ray image acquisition modes; and residualimage correction means for correcting residual image data contained inan X-ray image in the actual measurement from the X-ray flat paneldetector, using the residual image data stored in the storage means. 2.The X-ray image diagnostic apparatus according to claim 1, wherein theimage processing portion includes: an image memory that stores one frameof the residual image data from the X-ray flat panel detector; anattenuation quantity storage portion that stores quantities ofattenuation of first and subsequent frames of the residual image dataread out from the image memory; a computing unit that reads out thequantities of attenuation of the first and subsequent frames of theresidual image data in response to a time on the basis of one frame ofthe residual image data stored in the image memory, and subtracts theread quantities of attenuation of the residual image data from a signaloutputted from the X-ray flat panel detector; and a control portion thatcontrols the image memory, the attenuation quantity storage portion, andthe computing unit on the basis of respective signals, including controlsignals for each of the X-ray image acquisition modes including aradiographic signal and a fluoroscopic signal, and an imagesynchronizing signal to enable a display on the display means.
 3. TheX-ray image diagnostic apparatus according to claim 1, wherein: thestorage means stores plural frames of images of a residual image whileX-rays are shielded after an X-ray image is acquired at a specific X-raydose in advance.
 4. The X-ray image diagnostic apparatus according toclaim 1, wherein the image processing means includes: plural imagememories, each of which stores one frame of residual image data from theX-ray flat panel detector; plural attenuation quantity storage portionsthat store quantities of attenuation of first and subsequent frames ofthe residual image data read out from the image memories; a weightaddition quantity storage portion that reads out quantities ofattenuation of the first and subsequent frames of the residual imagedata in response to a time on the basis of one frame of the residualimage data stored in each of the image memories, subjects the readquantities of attenuation of residual images to weighting additiondepending on magnitude of a quantity of remaining residual images, andstores weight addition quantities; a computing unit that reads out theweight addition quantities stored in the weight addition quantitystorage portion in response to a time, and subtracts the read weightaddition quantities from a signal outputted from the X-ray flat paneldetector; and a control portion that controls the image memories, theattenuation quantity storage portions, and the weight addition quantitystorage portion on the basis of respective signals, including controlsignals for each of the X-ray image acquisition modes including aradiographic signal and a fluoroscopic signal, and an imagesynchronizing signal to enable a display on the display means.
 5. TheX-ray image diagnostic apparatus according to claim 1, wherein the imageprocessing portion includes: an image memory that stores one frame ofresidual image data from the X-ray flat panel detector; a first switchthat switches an output of a quantity attenuation of an image of aresidual image read out from the image memory depending on a read pixelmatrix of the X-ray flat panel detector; plural attenuation quantitystorage portions, each of which stores quantities of attenuation offirst and subsequent frames of the residual image data on the basis ofone frame from the image memory switched by the first switch, incorrespondence with the read pixel matrix of the X-ray flat paneldetector; a second switch that reads out a quantity of attenuation of aresidual image stored in the attenuation quantity storage portions inresponse to a time, and makes a switch to the read quantity ofattenuation of the residual image data; a computing unit that subtractsthe quantity of attenuation of the residual image data switched by thesecond switch from a signal outputted from the X-ray flat paneldetector; and a control portion that controls the image memory, theattenuation quantity storage portions, and the first and second switcheson the basis of respective signals, including control signals for eachof the X-ray image acquisition modes including a radiographic signal anda fluoroscopic signal, and an image synchronizing signal to enable adisplay on the display means.
 6. The X-ray image diagnostic apparatusaccording to claim 1, wherein the image processing means includes: animage memory that stores one frame of residual image data from the X-rayflat panel detector; a first switch that switches an output of aquantity of attenuation of a residual image read out from the imagememory depending on whether the X-ray image acquisition mode is a singleradiographic mode or a continuous radiographic mode; plural attenuationquantity storage portions, each of which stores quantities ofattenuation of first and subsequent frames of the residual image data onthe basis of one frame from the image memory switched by the firstswitch, in correspondence with the single radiographic mode and thecontinuous radiographic mode; a second switch that reads out a quantityof attenuation of the residual image stored in the attenuation quantitystorage portions in response to a time depending on the singleradiographic mode or the continuous radiographic mode, and makes aswitch to the read quantity of attenuation of the residual image; acomputing unit that subtracts the quantity of attenuation of theresidual image switched by the second switch from a signal outputtedfrom the X-ray flat panel detector; and a control portion that controlsthe image memory, the attenuation quantity storage portions, and thefirst and second switches on the basis of respective signals, includingcontrol signals for each of the X-ray image acquisition modes includinga radiographic signal and a fluoroscopic signal, and an imagesynchronizing signal to enable a display on the display means.
 7. TheX-ray image diagnostic apparatus according to claim 6, wherein: thecontrol portion determines a quantity of the residual image generatedfrom continuous exposures in response to an exposure time in thecontinuous radiographic mode.